Carbonyl difluoride is a useful material having various uses such as a material for fluoroorganic compounds, a cleaning gas for use in fabricating semiconductors, etc.
Examples of known methods for producing carbonyl difluoride using carbon monoxide as a starting material include methods wherein carbon monoxide is subjected to electrolytic fluorination (Patent Document 1), and wherein carbon monoxide is directly fluorinated using fluorine gas (Non-Patent Document 1). Examples of known methods using phosgene as a starting material include methods wherein phosgene is fluorinated using hydrogen fluoride in the presence of solvent, phosgene is fluorinated using hydrogen fluoride in the presence of solvent and triethylamine (Patent Document 2), phosgene is fluorinated using sodium fluoride in a solvent (Patent Document 3), and phosgene is fluorinated in the vapor phase using hydrogen fluoride together with an activated carbon catalyst (Patent Document 4). It is also known that carbonyl difluoride can be produced by reacting tetrafluoroethylene (TFE) with oxygen (Patent Document 5).
However, electrolytic fluorination and direct fluorination, which are methods for producing carbonyl difluoride using carbon monoxide as a starting material, require an expensive electrolytic vessel and/or a large facility for controlling the large amount of reaction heat, and are thus not preferable for industrial use. In electrolytic fluorination of carbon monoxide, CF4 and CF3OF are produced as byproducts, and in direct fluorination of carbon monoxide, CF3OF and like peroxides are generated as byproducts. Furthermore, the selectivity for carbonyl difluoride is low. Among the methods using phosgene, particularly in methods wherein phosgene is fluorinated using hydrogen fluoride in the presence of solvent, and methods wherein phosgene is fluorinated using hydrogen fluoride and an activated carbon catalyst, it is difficult to separate the generated carbonyl difluoride from hydrogen chloride because they have a small difference in boiling points (about 1° C.). In methods wherein phosgene is fluorinated using hydrogen fluoride in the presence of solvent and triethylamine or methods wherein phosgene is fluorinated using sodium fluoride in the presence of solvent, carbonyl difluoride can be obtained without generation of hydrogen chloride, but large amounts of triethylamine hydrochloride and sodium chloride are generated and therefore waste treatment and/or reuse/recycling thereof is necessary.
The reaction wherein TFE is oxidized using oxygen generates an extremely large amount of reaction heat, and therefore there is a risk of an explosion.
Furthermore, it is difficult to obtain large amounts of carbon monoxide, phosgene, and TFE, as are used in the above-mentioned production methods, because they are toxic and/or unstable, and careful handling is required.
Examples of readily obtainable materials include chlorodifluoromethane (HCFC22), and trifluoromethane (HFC23). Known production methods using these starting materials include: reacting HCFC22 or like monohalo-difluoromethane with oxygen (Patent Document 6), and reacting HCFC22 with ozone (Non-Patent Document 2). It is also known, although not as a production method, that carbonyl difluoride can be generated by reacting HFC23 with O(1D), which is an electronically excited oxygen atom (Non-Patent Document 3).
In Patent Document 6, generation of carbonyl difluoride was confirmed but not quantified. Patent Document 6 nowhere discloses what byproducts were generated. In Non-Patent Document 2, in addition to carbonyl difluoride, HCl, Cl2, and unidentified byproducts are generated. Here, the obtained HCl has a boiling point near that of carbonyl difluoride, and therefore it is difficult to separate the HCl from the carbonyl difluoride. HFC23 is a trihalogenated methane similar to HCFC22; however, it is known that HFC23 does not cause generation of HCl as a byproduct, because it does not contain chlorine, and the reactivity of HFC23 is very different from that of HCFC22. For example, their lifetimes in air according to the IPCC (evaluated based on the reaction speed with an OH radical, which is an oxidizing agent stronger than O2) (Non-Patent Document 4) are as follows. The lifetime of HCFC22 is 11.9 years, that of HFC23 is 260 years, and that of CHBrF2, which is an example of another trihalogenated methane, is 7 years. It is known that, compared to other trihalogenated methanes, HFC23 has an extremely low reactivity. Therefore, it is impossible to predict that carbonyl difluoride can be formed from HFC23 using the same methods as disclosed in Patent Document 6 and Non-Patent Document 2. The method disclosed in Non-Patent Document 3 uses a reaction with highly excited oxygen, and is fundamentally different from that of the present invention. Furthermore, it is industrially difficult to put the method disclosed in Non-Patent Document 3 to practical use, and, as with Patent Document 6, quantification was not conducted. According to Non-Patent Document 3, CO2 is excited by laser, O(3P) is generated in addition to O(1D), and O(3P) does not relate to the reaction with HFC23. It is known that O(1D) generates carbonyl difluoride by reacting with HFC23, and is then changed to O(3p) by being deactivated due to collision with the generated carbonyl difluoride (Non-Patent Document 5). This is not very efficient reaction. It is also known that O(1D) reacts with carbonyl difluoride and some portion thereof decomposes into CO2 and F2 (Non-Patent Document 5); however, because F2 is more oxidative than O2, when carbonyl difluoride is reacted with O2, carbonyl difluoride does not decompose into CO2 and F2.
As described above, many methods for producing carbonyl difluoride, including methods using fluorinated methane compounds as starting materials, have been published; however, a reaction achieving a high yield through a simple method has not yet been founded.
[Patent Document 1] Japanese Examined Patent Publication No. S45-26611
[Patent Document 2] Japanese Unexamined Patent Publication No. S54-158396
[Patent Document 3] U.S. Pat. No. 3,088,975
[Patent Document 4] U.S. Pat. No. 2,836,622
[Patent Document 5] U.S. Pat. No. 3,639,429
[Patent Document 6] EP0310255
[Non-Patent Document 1] J. Am. Chem. Soc., Vol. 91, (1969) pp. 4432-4436
[Non-Patent Document 2] Chemical Abstracts Vol. 93, No. 13, (1980), p. 621 Abstracts No. 132037x
[Non-Patent Document 3] Chemistry Letters (1992), pp. 1309-1312
[Non-Patent Document 4] Climate Change 2001: The Scientific Basis
[Non-Patent Document 5] Chemical Physics Letters Vol. 69, (1983), pp. 129-132
[Non-Patent Document 6] Zeitschrift fur Anorganische und Allgemeine Chemie Vol. 242, (1939), pp. 272-276